In motor vehicles, sensor clusters are used for recording the vehicle environment. In particular, sensor clusters are used in driver assistance systems.
To provide data for such driver assistance systems, the use of sensor clusters in motor vehicles is becoming more and more common, sometimes comprising different technology sensors, the ranges of which may at least partially overlap. In particular, the use of sensor clusters that are made up of two different sensors, one narrow beam sensor, such as e.g. a Radio Detection And Ranging (RADAR) technology sensor or a Light Detection And Ranging (LIDAR) technology sensor or other sensor based on Light Amplification by Stimulated Emission of Radiation (LASER) technology, and one imaging sensor, both of which covers essentially the same scene.
Sensor clusters of the kind comprising a narrow beam technology sensor and at least one imaging sensor are usually arranged in a vehicle at the inside of a windshield in the vicinity of a rear-view mirror and such that the sensors of the cluster are forward looking, in relation to the normal direction of travel of the vehicle.
Alignment of the narrow beam sensor of the sensor cluster with respect to the geometrical travel axis of the motor vehicle is critical for its proper operation, and must therefore normally be done such that the deviation from this axis lies within ±1°. In order to meet these demands this kind of sensor clusters are normally calibrated at a designated station during vehicle manufacture or at a special calibration workshop for replacement and repairs. The demands for such a designated station are strict, e.g. the floor thereof has to be perfectly level and horizontal and the vehicle, for which calibration is to be performed, often has to be placed perfectly positioned and aligned at this floor, such that the relation to special calibration targets is ensured. Upon calibration the sensors of the sensor cluster of the perfectly placed and aligned vehicle are calibrated towards the special calibration targets. Accurate alignment with the vehicle is tedious and requires special instrumental technology.
As is evident from the above description this calibration process is both cumbersome and costly, in addition to requiring such special facilities that, for e.g. cost reasons, cannot be provided at more than a few specialized repair-shops, necessitating sometimes lengthy and costly trips to have a sensor cluster calibrated following replacement thereof or replacement of the windshield to which it is mounted.
Several attempts have been made to facilitate calibration of vehicle mounted sensors without relying on such costly and sparsely available dedicated calibration stations. One such attempt is illustrated by US2009033926, which relates to a device for calibrating an imaging sensor system in a motor vehicle. This is accomplished according to US2009033926 by providing a calibration object on the inside of an engine hood of the vehicle in such a way that after raising the engine hood, the calibration object is within detection range of the imaging sensor system and in the depth-of-field range of the imaging sensor of the image detection system. Due to the location of the calibration object on the inside of the engine hood, no external calibration object is necessary. This is said to yield cost advantages in the manufacture of the vehicle, in the repair shop, and also for the owner of the vehicle because the imaging sensor system may be calibrated for the first time without the use of complex external instrument technology and may be recalibrated at any time, if necessary.
Although the calibration device suggested by US2009033926 may for some applications provide for sufficient calibration of an imaging sensor, the device of US2009033926 is not suitable for the calibration of sensor clusters comprising multiple sensors, which, due to e.g. differences in alignment between sensors of different sensor clusters may provide insufficient alignment for proper functioning of certain kinds of sensors, such as narrow beam sensors, e.g. RADAR, LIDAR or LASER technology based sensors.